# std::is_compound

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< cpp‎ | types

Defined in header `<type_traits>` |  |
template< class T > struct is_compound; |  | (since C++11)

`std::is_compound` is a UnaryTypeTrait.

If `T` is a compound type (that is, array, function, object pointer, function pointer, member object pointer, member function pointer, reference, class, union, or enumeration, including any cv-qualified variants), provides the member constant `value` equal true. For any other type, `value` is false.

If the program adds specializations for `std::is_compound` or `std::is_compound_v`, the behavior is undefined.

### Template parameters

T | - | a type to check

### Helper variable template

template< class T > constexpr bool is_compound_v = is_compound<T>::value; |  | (since C++17)

## Inherited from std::integral_constant

### Member constants

value [static] | true if `T` is a compound type, false otherwise (public static member constant)

### Member functions

operator bool | converts the object to bool, returns value (public member function)
operator() (C++14) | returns value (public member function)

### Member types

Type | Definition
`value_type` | bool
`type` | std::integral_constant<bool, value>

### Notes

Compound types are the types that are constructed from fundamental types. Any C++ type is either fundamental or compound.

### Possible implementation

    template<class T>
    struct is_compound : std::integral_constant<bool, !std::is_fundamental<T>::value> {};

### Example

Run this code

    #include <type_traits>
    #include <iostream>

    static_assert(not std::is_compound_v<int>);
    static_assert(std::is_compound_v<int*>);
    static_assert(std::is_compound_v<int&>);

    void f();
    static_assert(std::is_compound_v<decltype(f)>);
    static_assert(std::is_compound_v<decltype(&f)>);

    static_assert(std::is_compound_v<char[100]>);

    class C {};
    static_assert(std::is_compound_v<C>);

    union U {};
    static_assert(std::is_compound_v<U>);

    enum struct E { e };
    static_assert(std::is_compound_v<E>);
    static_assert(std::is_compound_v<decltype(E::e)>);

    struct S
    {
        int i : 8;
        int j;
        void foo();
    };
    static_assert(not std::is_compound_v<decltype(S::i)>);
    static_assert(not std::is_compound_v<decltype(S::j)>);
    static_assert(std::is_compound_v<decltype(&S::j)>);
    static_assert(std::is_compound_v<decltype(&S::foo)>);

    int main()
    {
        std::cout << "All checks have passed\n";
    }

### See also

is_fundamental (C++11) | checks if a type is a fundamental type (class template)
is_scalar (C++11) | checks if a type is a scalar type (class template)
is_object (C++11) | checks if a type is an object type (class template)
is_array (C++11) | checks if a type is an array type (class template)

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